1. Technical Field
The present invention pertains to methods and apparatus utilized in surgical procedures involving fixation of soft tissue to bone and, more particularly, to a novel method and apparatus for anchoring sutures to bone tissue to permit the aforesaid fixation.
2. Discussion of the Prior Art
As part of various endoscopic or arthroscopic surgical procedures, it is necessary to permanently attach a suture to bone tissue. For example, in certain procedures requiring suturing of soft tissue (e.g., muscle, cartilage, tendons, ligaments, etc.) to bone tissue, the suture must be anchored to the bone tissue before suturing can proceed. The prior art includes numerous suture anchors adapted to be secured in pre-drilled holes or tunnels in the bone tissue, and most of these anchors have one or more disadvantageous characteristics. Some prior art suture anchors are required to be hammered into a bone tunnel. These anchors are exemplified by U.S. Pat. Nos. 5,102,421 (Anspach, Jr.); No. 5,141,520 (Goble et al); and No. 5,100,417 (Cerier et al). Hammering (or impacting as it is often described) has the disadvantage of potential trauma and damage to surrounding bone tissue, and has limited applicability where the location of the bone tunnel is not axially aligned with an arthroscopic portal to direct transmission of the impacting force through an impactor to an anchor.
Some prior art suture anchors are threadedly mounted in the bone tunnel, as exemplified by U.S. Pat. Nos. 5,156,616 (Meadows et al) and No. 4,632,100 (Somers et al). The screw insertion procedure tends to be time-consuming in that a pilot hole must first be drilled into the bone and then the hole may have to be tapped to receive the screw. If, as sometimes happens, the surgeon determines that the tunnel is not ideally located, the drilling and tapping of another pilot hole becomes necessary, thereby requiring additional steps in an already lengthy procedure.
Many suture anchors involve an insertion procedure wherein a relatively large insertion tool must partially enter the bone tunnel along with the anchor, thereby requiring a larger diameter tunnel than would be necessary for the anchor alone. Examples of such suture anchors are found in U.S. Pat. Nos. 5,037,422 (Hayhurst et al); No. 4,741,330 (Hayhurst); No. 4,968,315 (Gatturna) and No. 4,899,743 (Nicholson et al). Large diameter bone tunnels for receiving suture are undesirable in many applications, particularly where the bone itself is relatively small. In addition to the insertion tool size, some anchors themselves must be so large as to limit the degree to which bone tunnel diameters can be decreased. An example of such an anchor is found in U.S. Pat. No. 5,224,946 (Hayhurst et al).
Most of the foregoing exemplar prior art suture anchors suffer from the disadvantage of being automatically deployed upon initial insertion into the bone tunnel. Specifically, such anchors typically have permanently projecting resilient barbs, or the like, that are forced into the tunnel during initial insertion and preclude proximally directed movement within the tunnel after at least one barb engages the surrounding bone tissue during insertion. If the particular bone tunnel turns out to be unsuitable, either because of location or configuration, the surgeon may not recognize this until after the anchor has been inserted. With many prior art anchors there is no possibility of removing the inserted anchor; thus, a new tunnel must be drilled and a second anchor inserted. Accordingly, two (or possibly more) anchors may be left at the surgical site, and only one of the anchors is functional. This problem is addressed in U.S. Pat. No. 5,176,682 (Chow) wherein a generally cylindrical suture anchor is disclosed as having normally retracted fins capable of being selectively projected radially to engage the bone tunnel wall in a barb-like manner. Selective projection of the fins is effected by hammering a pin axially through the anchor to force the fins radially outward. Prior to hammering the pin, the inserted anchor is readily removable from the bone tunnel, thereby permitting the surgeon to test the adequacy of the drilled tunnel and its location. If a tunnel is unsatisfactory, the anchor can be removed, rather than being left in place. Although this technique solves the problem of having an unused anchor left in an unsatisfactory tunnel, it has some other disadvantages. In particular, the cylindrical body of the Chow anchor must be specially contoured with longitudinally extending recessed channels for accommodating the anchored suture or ligament without compressing it between the anchor and the bone tunnel wall. Such compression could unduly stress the suture or ligament and cause it to tear. Occasionally, the suture becomes dislodged from the recess and becomes stressed in spite of the presence of the recesses. Moreover, the channels add complexity to the manufacture of the anchor. In addition, the actuator pin for the Chow anchor is not positively retained by the anchor, leaving the possibility that the pin will inadvertently become dislodged, permitting the fins to retract and the anchor to become disengaged from the tunnel. Also, the insertion tool threadedly engages the anchor during insertion, thereby requiring multiple rotations of the inserted tool to disengage it from the anchor after insertion. Still further, the insertion procedure for the Chow anchor requires a mallet, in addition to the insertion tool, to hammer the pin through the insertion tool (serving as a guide) and into the anchor. Thereafter, the insertion tool must be removed in a manner described ambiguously at best in the Chow patent. The installation procedure and tools tend to be unnecessarily complicated.